In many orthopaedic surgical procedures, bone cements are used to fix implants to the bone. Conventional bone cements are generally polymeric materials, which are prepared by copolymerization of its components as needed. Bone cement is prepared by copolymerizing a liquid monomer and a powdered copolymer, such as methyl methacrylate and polymethyl methacrylate or methyl methacrylate-styrene. During mixing of the constituent components of the cement, air bubbles may be formed within the cement. It is thought that to improve the resultant strength of the cement, the air bubbles must be evacuated from the mixture to ensure a uniform reaction product. Consequently, the mixing of the constituent components is ideally performed in a vacuum.
The separate constituent components may be mixed within a mixing cartridge as is well known in the art. The mixing cartridge, when fully extended, provides a larger volume for mixing the constituent components to ensure that the constituent components are adequately mixed. Such mixing cartridges are generally enclosed by removable caps, which include a valved port for connection to a vacuum pump. Vacuum pumps draw a vacuum within the cartridges during the mixing process to reduce the occurrences of air bubbles within the cement. The caps have an off-set outlet port through which the mixed cement compound is expelled and a central opening through which an agitator is reciprocally disposed. The agitator has an elongated shaft and a mixing paddle for mixing the constituent components. The agitator shaft is broken off after mixing and the offset outlet port is opened to expel the cement. In a prior art vacuum cartridge mixing device, an end plunger is released after mixing yet while the cartridge is still under a vacuum. The vacuum pressure within the cartridge causes the plunger to be drawn into the cartridge to collect the cement. The plunger stops moving within the cartridge when the force exerted by the vacuum equalizes. After the cement is throughly mixed, the agitator shaft is broken off and the cartridge is inserted into a conventional cement applicator gun. Cement applicator guns are well known in the art. Generally, a variety of cement nozzles are affixed to the outlet port to aid in the application of the cement within the bone cavity. Because the outlet port is off center, a certain amount of cement cannot be expelled from the cartridge, and is discarded with the disposal of the cartridge.
Heretofore, the various cement constituent components and mixing apparatus have been individually packaged and provided to the user. Since the cement sets rapidly, the preparation and application of bone cement is time critical. Preparation of bone cement is generally performed in the sterile field of the operating room. Consequently, each piece of apparatus must be provided in a sterile package. Providing all of the various mixing apparatus and cement constituent components as a single preassembled collection or kit would be more convenient for the users in the operating room.